Pretreatment of catalyst used in the production of acrylic acid and acrolein

ABSTRACT

A CATALYST OF SB, V AND SN AND/OR FE USED IN THE OXIDATION OF PROPYLENE TO ACRYLIC ACID AND ACROLEIN IS HEATED TO REACTION TEMPERATURE FOR AT LEAST ONE HOUR IN A OXYGENFREE REDUCING ATMOSPHERE, IN ORDER TO AVOID UNDESIRABLE TEMPERATURE PEAKS IN THE CATALYST BED.

United States Patent 3,554,931 PRETREATMENT OF CATALYST USED IN THEPRODUCTION OF ACRYLIC ACID AND ACROLEIN Christopher John Brown,Walton-on-the-Hill, Ta'dworth, England, assignor to BP Chemicals (U.K.)Limited, London, England, a British company No Drawing. Originalapplication Nov. 22, 1965, Ser. No. 509,155, now Patent No.3,403,177,dated Sept. 24, 1968. Divided and this application May 31,1968, Ser. No. 733,283

3,554,931 Patented Jan. 12, 1971 comprises the oxidation of propylenewith molecular oxy- Claims priority, application GreatBritain, Nov. 26,1964,

48,035/ 64 The portion of the termof the patent subsequent to Sept. 24,1985, has been disclaimed,

Int. Cl. B01j 11/06, 11/22 US. Cl. 252-472 ABSTRACT OF THE DISCLOSURE 7A catalyst of Sb, V and Sn and/ or Fe used in the oxida- 6 Claims tionof propylene to acrylic acid and acrolein is heated to reactiontemperature for at least'one hour in a oxygenfree reducing atmosphere,in order to-avoidundesirable temperature peaks in the catalyst bed.

This is a divisional application of copending applica tion U.S. Ser. No.509,155, filed Nov. 22, 1965, now US. Pat. No. 3,403,177, issued onSept. 24, 1968.

The present invention relates to a process for the production ofunsaturated aliphatic carboxylic acids and in particular to theproduction of acrylic acid.

Our copending application Ser. No. 427,502 describes a process for theproduction of acrylic acid with or without acrolein by reaction ofacrolein or compounds giving rise to acrolein under the reactionconditions, for example, propylene or allyl alcohol in the presence ofmolecular oxygen in the vapour phase at an elevated temperature over anoxide composition containing antimony, vanadium, with or without one ormore additional polyvalent metals such as tin, titanium, chromium,manganese, iron, cobalt, nickel, copper, zinc, molybdenum, cadmiumtungsten or thorium as catalyst.

It has been found that of these catalysts those containing antimony,vanadium and at least one other polyvalent metal, for example, tinand/or iron have particular advantage in catalysing the production ofacrylic acid together with acrolein from a propylene feedstock. Thereaction temperature in such a process varies within the range 250*0 C.It has been observed that on commencement or start-up of the process thecatalyst is endangered because high temperature peaks develop in the bedand, a high content of the oxides of carbon is present in the reactoreffluent. Avoidance of this condition has hitherto only been possible byaging the catalyst at temperatures below 300 C., for example, of theorder of 250 C., and thereafter gradually increasing the temperatureover a long period, for example, 30-50 hours until optimum reactiontemperatures are reached. Similar startup difliculties also arise if thepropylene feed is interrupted and the air/stream mixture passed over thecatalyst for some time. Having regard to the conditions operating on acommercial plant, such a method of start-up is impracticable.

7 It is an object of the present invention to overcome the abovedisadvantage and to provide a method of start-up of the process whichavoids the necessity of a gradual build-up of temperature to a finaloptimum.

Accordingly, the present invention is a process for the production ofacrylic acid together with acrolein which gen in the vapour phase at atemperature in the range 250- 500" C. in the presence of an oxidecomposition containing antimony, vanadium, and a metal selected from thegroup consisting of tinor iron or mixtures as catalyst, characterized inthat the catalyst is heated in an oxygenfree reducing atmosphere toreaction temperature for a period of at least one hour beforecommencement of the oxidation reaction.

It has been found possible by operation in accordance with the aboveinvention to obtain optimum yields of acrylic acid immediately oncommencement of the oxidation process and without initial production oflarge amounts of the oxides of carbon in the reactor efiluent.

The oxygen-free reducing atmosphere may be hydrogen or propylenestarting material. Preferably the atmosphere comprises propylene andsteam. The catalyst is heated in this atmosphere at reactiontemperature, that is to say, at temperatures subsequently to be used forthe oxidation reaction for a period of at least one hour and preferablytwo hours before commencement of the oxidation. In operation, forexample, the catalyst bed is contacted with a gaseous mixture containingpropylene and steam and thereafter the oxygen is supplied together with,if necessary, an increased concentration of propylene for the oxidationreaction over the pretreated catalyst.

The catalyst used in the present process may be regarded as a mixture ofantimony and vanadium oxides with the oxides of tin and/ or iron or asoxygen containing compounds of antimony, vanadium and iron and/or tin;under the reaction conditions such a catalyst may contain either or bothforms.

The catalyst may be prepared, for instance, by intimately mixing theoxides (or compounds yielding the oxides on decomposition) of antimonyand vanadium 'with the oxides or compounds of iron and/or tin, or byco-hydrolysis of ater soluble salts, for example, by the addition ofammonia to an aqueous solution of the chlorides. The iron and tin oxidesor compounds may be added during or after the admixture of the antimonyand vanadium oxides or compounds. Oxides of antimony which may be usedin the manufacture of the catalyst include antimony trioxide, antimonytetroxide, antimony pent oxide or mixtures of these oxides. Suitableoxides of tin may be, for example, metastannic acid or stannic oxide.

The proportions of the various components of the catalyst may varywithin moderately wide limits. Suitably the composition containspreferably a molar excess of antimony over any other single componentand a molar ratio of antimony to vanadium between 1.8 and 3.5 ispreferred.

By whichever method the catalyst is prepared its activity is frequentlyimproved by a prior heat treatment, for instance, at a temperaturebetween 55 0-1100" C., in a molecular oxygen containing gas.

The catalyst used in the process of the present invention may, ifdesired, be deposited on supports such as alumina, silica or titania.

The proportion of propylene in the feed during the oxidation reactionmay vary within fairly wide limits, for example, between l20% by volumeof the feed and suitably between 210% by volume.

The concentration of oxygen in the feed may also vary within moderatelywide limits, for example, between 1-20% by volume and preferably between2-15% by volume. The oxygen may be diluted with inert gases, forexample, nitrogen, steam and may be, for example, supplied as air.

The acrylic acid may be recovered from the reaction products in anysuitable manner, for example, by extraction with a solvent such aswater.

The invention is illustrated by the following example:

EXAMPLE A mixture of propylene, v./v.; steam, 35% v./v. and air, 60%v./v. was passed at 4 seconds contact time to a reactor packed with acatalyst consisting of the oxides of antimony, tin, vanadium and iron,and surrounded by heat-transfer salt at 332 C. temperature peak rapidlydeveloped (70 in 3 minutes) in the catalyst bed and the propylene feedWas turned olf (carbon oxides yield 30 The reactor was charged withfresh catalyst and a mixture of propylene (53 l./hr.) and steam (400l./hr.) passed through at 315 C. for 45 minutes. Attempts to apply fullfeeds to the reactor caused an unstable temperature peak to develop dueto insufficient reduction in catalyst activity. After a further45-minute period of reduction with propylene and steam, full feeds wereapplied to the reactor at 320 C. (salt temperature) and a temperaturepeak of only 25 developed in the catalyst bed. Based on the propylenefeed, the following yields were obtained, acrylic acid, 14.2%; acrolein,45.2%; saturated acids, 2.3%; saturated carbonyls, 0.1%; carbon oxides,8.3%.

What is claimed is:

1. A process for preparing a catalytic composition which comprisesforming an oxide composition consisting essentially of antimony,vanadium and at least one metal selected from the group consisting oftin and iron, and wherein antimony is in molar excess over any othersingle metal component and the molar ratio of antimony to vanadium isbetween about 1.8 to 3.5, and heating said catalyst oxide composition inthe range of 250500 C. in a reducing atmosphere for a period of at leastone hour.

2. A process as claimed in claim 1 wherein the catalyst is heated in thereducing atmosphere for at least two hours.

3. A process as claimed in claim 1 wherein the reducing atmospherecomprises hydrogen.

4. A process as claimed in claim 1 wherein the reducing atmospherecomprises propylene.

5. A process as claimed in claim 1 wherein the reducing atmospherecomprises a mixture of propylene and steam.

6. A catalyst composition prepared by the process defined in claim 1.

References Cited UNITED STATES PATENTS 3,358,020 12/1967 Hendrickx260530 3,210,295 /1965 'Modiano 252--46l 3,197,419 7/1965 Callahan252456 3,403,177 9/1968 Brown 260-533 DANIEL E. WYMAN, Primary ExaminerP. M. FRENCH, Assistant Examiner US. Cl. X.R. 252-461, 464, 466

